This invention relates to filtering equipment and more particularly to filter press systems used, for instance, in the mining, agricultural, waste management, food, chemical, pharmaceutical industries, pulp and paper industries.
Filter presses (also called “plate-and-frame”, “chamber”, “membrane”, or “membrane plate” filter presses) separate liquids and solids by forcing the liquid fraction of a feed slurry through a permeable filter cloth. The separation takes place in chambers formed between the recessed faces of plates, which have been clamped together in a rugged steel frame. The molded filter plates are formed with corrugated drainage surfaces in the chamber recesses, and ports are provided for slurry feed and filtrate drainage. Each face is covered with a filter cloth and the plates are clamped together using a hydraulic ram. Slurry is pumped in under high pressure, filling the chambers with solids and pushing liquid out through the filter cloth. When no more solids can be forced into chambers, the feed pumps are turned off and compressed air or steam is used to remove interstitial water from pores in the formed filter cake. When the desired residual moisture content has been achieved, the filter is opened, cake is removed by gravity, and the procedure is repeated.
Additions to the basic filtration cycle may include the removal of residual slurry from the feed channel with compressed air and/or water, air purging of filtrate drain channels, and cake or filter cloth washing to remove soluble impurities. Very high solids concentrations can be achieved in cakes of low permeability through the use of filter plates lined with optional elastomeric membranes. After the basic filtration cycle has been completed, these membranes are inflated with pressurized air or liquid, squeezing additional moisture from the filter cake.
Many processes in the food, chemical or pharmaceutical industries make products from liquid-solid suspensions or slurries which contain solids which do not dissolve and are suspended in the liquid fraction. Filter presses separate the solids from the liquids so that the useful part can be processed, packaged or delivered to the next step.
Filter presses generally work in a “batch” manner. After filter case is removed from the press, it is re-loaded with slurry and the filtering cycle repeated. Typically, filter presses use pressures capable of producing filter cakes having water content under 25%. Filter chambers may comprise square, rectangular, or round filter plates supported in a frame. Once the filter chambers are loaded with slurry, the filter plates are forced together with hydraulic rams that generate pressures around 225 pounds per square inch (approximately 1,551,000 Pascal).
Formed filter cake further enhances removal of fine particles in the introduced slurry and therefore contributes to filtrate clarity. Filtrate can be drained away for safe disposal, or it can be kept in a water tank for recycled use. At the end of filtration, solid filter cakes are removed by gravity as the plates are separated. In some designs shaker mechanisms are used to shed and break up the filter cake. The whole filtration process is often controlled by electronics and operated automatically or semi-automatically.
Due to the large number of plates per machine, high pressures involved, and unpredictability of mechanical and dynamic slurry feed properties, manufacturers are currently limited in the achievable output tonnages per filter press. Moreover, state-of-the-art manufacturing processes limit the size of each plate to a maximum of 3200 mm by 2400 mm.